1. Field
The present invention relates generally to decoding of variable-length prefix codes, e.g., Huffman codes, and, more specifically, to a new decoding scheme for codes whose prefixes are formed by a regular bit pattern.
2. Description
Entropy coding is a widely used data compression technique that many video and audio coding standards are based on. The theoretical basis of entropy coding states that a compression effect can be reached when the most frequently used data are coded with a fewer number of bits than the number of bits denoting the less frequently appearing data. This approach results in coded data streams composed of codes having different lengths.
There are a number of methods to form such variable length codes. One popular method uses a prefixed coding in which a code consists of a prefix that allows a decoding system to distinguish between different codes, and several significant bits representing a particular value (e.g., Huffman coding).
While most coding standards employ Huffman codes with prefixes composed of a series of ‘1’ or ‘0’ bits in their coding schemes, some standards (e.g., ISO/IEC 14496-2, Moving Pictures Experts Group (MPEG)-4 coding standard, Visual) allow for codes prefixed with a series of longer bit patterns. As a general rule, the number of bits that comprise a variable length code depends on the number of bits that comprise the prefix of the code.
Therefore, a need exists for the capability to provide high speed decoding of variable length codes prefixed with regular combinations of bits.